Integrated retrieval of ocean surface wind and current fields from single-geometry SAR observations through a physically constrained Bayesian framework

This is the authors' abstract. We don't add key points for this paper.

Ocean surface winds and currents are coupled through air–sea interaction but are commonly retrieved independently from spaceborne synthetic aperture radar (SAR). For operational single-geometry SAR, simultaneous wind–current retrieval is underdetermined and remains reliant on background information. We propose a physically constrained Bayesian framework that combines radar backscatter and Doppler centroid anomaly measurements to retrieve 10-m wind and radial surface current. An empirical wind-drift relation softly constrains the radial-current increment relative to a product-derived background current, and the solution is obtained by weighted maximum a posteriori estimation. The framework is evaluated using multi-year Sentinel-1 observations collocated with scatterometer, buoy, and high-frequency radar measurements across different sea states. Parameters calibrated in a Gulf Stream-influenced U.S. East Coast region are fixed for temporally held-out events and an independent Southern California test. Across the East Coast data, wind-speed root-mean-square difference (RMSD) decreases by 0.59 − 0.77 m s − 1 relative to ERA5 atmospheric reanalysis. Against high-frequency radar, radial-current RMSD is 0.21 m s − 1 , compared with 0.59 m s − 1 for the operational Sentinel-1 radial-velocity product, 0.48 m s − 1 after a conventional wind-wave Doppler correction, and 0.38 m s − 1 for an ocean-model projection. Event-level ablations show that the physical constraint provides further RMSD reductions of 0.171 m s − 1 and 0.324 m s − 1 in the two independent tests. These results isolate radial-current skill attributable to the physical term beyond joint data fusion alone and demonstrate the value of jointly exploiting complementary SAR observables. The framework provides a practical pathway toward joint kilometer-scale mapping of coastal winds and radial currents from routine single-geometry acquisitions.